Welcome to MobileRead, richard friedman. From you users guide
Built-in PDF Reader for Kindle DX
"Your Kindle DX can display PDF documents without losing the formatting of the original file. Send PDF documents directly to your Kindle (via your @Kindle address) or drag and drop PDF files from your computer to your Kindle (when connected via USB). You can also magnify PDFs by viewing them in landscape mode.
Some features are not currently supported, including annotations and Text-to-Speech. The only Kindle devices supported for PDFs are the Kindle and Kindle DX."
Here is the help page where you can download the users guide in pdf to 'read along'